A. E. Feiring, Journal of Fluorine Chemistry, 13, 7-18 (1979) discloses using TaF.sub.5 as a halogen exchange catalyst for adding HF to tetra and trichloroethene and related compounds. The catalyst is also useful in fluorine-chlorine exchange reactions. The use of TaF.sub.5 as a catalyst for the addition of HF to unsaturated compounds was also disclosed by U.S. Pat. No. 4,258,225 to Feiring. Optimum conditions for using tantalum pentafluoride (TaF.sub.5), or niobium pentafluoride (NbF.sub.5) in certain halogen exchange reactions was disclosed by U.S. Pat. No. 4,967,024 to Gumprecht (which corresponds to Canadian Patent No. 1,323,040. The disclosure of each of the above-identified references is hereby incorporated by reference.
U.S. Pat. Nos. 3,107,976, 3,117,833, 3,712939, 3,972,710, and 4,445,438 disclose processes for recovering tantalum and niobium from ore by digesting the ore, followed by extracting to recover metallic materials. The disclosure of these Patents is also hereby incorporated by reference.